This invention relates generally to the field of surfactants and more specifically to novel ether sulfonate surfactants, a process for making same, and applications for their use.
Surfactants are used for a wide variety of applications because their unique structures impart special properties to systems containing them. These properties include the ability to allow immiscible liquids such as oil and water to mix, to improve the wetting properties of a liquid on a solid, to allow solids to be suspended in liquids, and to foam liquids. It is for these reasons that surfactants find widespread use in many industries including, but not limited to, agriculture, adhesives, coatings, deinking, detergents, emulsion polymerization, laundry, lubricants, metal working, mining, oilfield, personal care, pharmaceuticals, and soil remediation.
Surfactants can be divided into four main classes by the charges they carry. The four classes are (1) nonionic surfactants having no charge, (2) anionic surfactants having a negative charge, (3) cationic surfactants having a positive charge, and (4) amphoteric surfactants having positive, negative or no charge depending on the pH of the system in which the surfactant is contained. The properties associated with the different types of surfactants are described in many articles and books including Rosen, Surfactants and Interfacial Phenomena, (1978). A compilation of most of the surfactants available along with their properties and a list of their manufacturers is available from McCutcheon's Emulsifiers and Detergents (2001).
Of the four classes of surfactants, anionic surfactants are found to have the most widespread uses and are produced in the largest volume. This is primarily due to their lower cost, better performance, and because of the applications where they are used such as laundry, personal care, household, institutional and industrial cleaning, agriculture and coatings, that tend to require large volumes of lower cost material made from readily available raw materials. The anionic surfactants are essentially various sulfates, sulfonates, phosphates, phosphonates, and carboxylates. The chemistry of these products is very well described in Anionic Surfactants-Organic Chemistry, Volume 56, Surfactant Science Series, Marcel Dekker (1995). Their physical properties are addressed in Anionic Surfactants-Physical Chemistry of Surfactant Action, Volume 11, Surfactant Science Series. Marcel Dekker (1981). The most common and widely used anionic surfactants are the sulfates and the sulfonates. These include alcohol sulfates, alcohol ether sulfates, glycerol sulfates, alkoxylated alkylphenol sulfates and sulfonates, alkylaryl sulfonates, alpha-olefin sulfonates, alkane sulfonates, and sulfosuccinates. Sulfonates are generally more thermally and hydrolytically stable then sulfates since the sulfur group is attached directly to a carbon. In sulfates, the sulfur group is attached to the carbon through an oxygen group. Thus sulfates can be considered esters of sulfuric acid and the hydrolysable ester bond makes them relative instability. This instability limits the conditions and applications where they can be used.
Ether sulfates contain not only a sulfate ester but also various amounts of ethylene, propylene, or butylene oxide, or mixtures of two or more of these. Due to the presence of additional hydrophilic alkyl oxides, the ether sulfates in general are more tolerant to electrolytes and divalent metal ions and are therefore useful where hard waters are encountered. Unfortunately the ether sulfates are also hydrolytically unstable and their uses are limited where high temperature or extreme pH conditions (high or low) are encountered.
One solution to this instability problem is to employ ether sulfonates. These surfactants are both salt tolerant and hydrolytically stable. Ether sulfonates have been reported to give excellent performance under conditions of high salinities, high temperatures and extreme pH conditions. Schwartz et al., Surface Active Agents and Detergents, Interscience Publishers, Vol. II p 74-75, refers to these desirable properties of ether sulfonates and discloses sulfonated polyethoxylated alkyl phenols and their method of preparation by reaction of an ethoxylated alkyl phenol with sodium ethanol sulfonate. In addition, Schwartz et al. discloses that ether-linked sulfonates may be prepared by the addition reaction of butane sultone with an alkyl phenol.
The prior art on the production of ether sulfonates is summarized below in Table 1
where:
                R=alkyl, alkenyl, phenyl, alkenylphenyl, amine,        R′=C2H4, C3H6 or C4H8, or mixtures of 2 or more of these,        R″=an alkenyl spacer        M=alkali or alkaline metal, ammonium or an amine        
TABLE 1R—O—(R′O)n —R″SO3MReferencenR″U.S. Pat. No.1 to 30C2H45,075,042U.S. Pat. No.0C8H16 to C22H443,424,693U.S. Pat. No.1 to 10C3H6 or C4H84,138,345U.S. Pat. No.1 to 13C2H4, C3H6, C4H8, or CH2(CH(OH))CH24,267,123U.S. Pat. No.2 to 20C2H44,293,428U.S. Pat. No.0 to 15C2H4, C3H6, or CH2(CH(OH))CH24,733,728This Invention1 to 30+C7H14 to C30H60
U.S. Pat. No. 5,075,042 issue to Allison et al. on Dec. 24, 1991 describes the preparation of aliphatic poly(ethyleneoxy)sulfonates by the chlorination with thionyl chloride of an ethoxylated aliphatic alcohol and subsequent conversion of the resulting chloride to the sulfonate with sodium sulfite. This patent goes on to reveal that certain aliphatic poly(ethyleneoxy)sulfonates are commercially available as AVANEL® S Anionic Surfactants.
BASF Corporation currently markets AVANEL® surfactants. Their literature describes alkyl ether sulfonates of C12-15 alkyl with 7 EO (AVANEL® S-70), with 15 EO (AVANEL® S-150 CG), and C8 alkyl with 3 EO (AVANEL® S-74) as “unique because the ethylene oxide gives certain nonionic characteristics to the products, and the sulfonate group provides certain anionic characteristics. These products are extremely stable over a wide range of pH and electrolyte concentrations.” The key features of the alkyl ether sulfonates, as pointed out by BASF, include excellent hard water tolerance, hydrolytic stability over the entire pH range, biodegradability, oxidative stability in hypochlorite and oxygen bleaches, thermal stability, high electrolyte tolerance, excellent rinsability, sheeting action, extreme mildness to the skin, good emulsification characteristics, and low critical micelle concentrations.
U.S. Pat. Nos. 3,424,693 and 3,424,694 issued to Stein, et al. on Jan. 28, 1969 discloses the reaction of partially neutralized olefin sulfonic acids containing 8 to 22 carbon atoms with a sultone reactive product and the recovery of the resulting mixture of surface-active compounds. Both these patents claim yields of between 10 and 50 mole percent for the reaction product of the sultone and sultone reactive compound with the remainder being the neutralized salt of olefin sulfonic acid. Alkoxylated products are not disclosed as sultone reactive starting materials in this patent. Ether sulfonates of alkylamines have been prepared in the past. Williams in U.S. Pat. No. 4,138,345 issued on Feb. 6, 1979, discloses the reaction of the metallic salts of alkoxylated or dialkoxylated amines with propane or butane sultone. These give the corresponding mono and di sulfonates of the amines and these have been found useful alone or in combination with other surfactants in the recovery of oil.
U.S. Pat. No. 4,267,123 issued to Chen et al. on May 12, 1981 states that “propane sulfonates of various amines and polyethoxylated alcohols are known surfactants. However, propane sulfonates of alcohols and thiols have only been prepared in the literature by reaction of alkali metal salts of alcohols and thiols with propane sultone. This is a convenient high yield laboratory synthesis but is not desirable on a large scale for several reasons. Foremost among them are the fact that (1) such a reaction requires multistep synthesis and purification of propane sultone, (2) propane sultone is expensive to purify and its overall yield of 80-90% limits the yield in the preparation of the propane sulfonates and (3) propane sultone is a known carcinogen.”
U.S. Pat. No. 4,293,428 issued to Gale, et al. on Oct. 6, 1981 involves the synthesis and application of alcohol ether sulfonates for oil recovery. This patent states that it has been determined that “positioning ethylene oxide and/or propylene oxide adjacent to the sulfonate group of a given surfactant tends to give it more water solubility and increases its tolerance to high concentrations of mono and di-valent salts”. In addition the ether sulfonates were found to exhibit very good resistance to hydrolysis in high-temperature reservoirs. A thorough discussion of their application in oil recovery is given in Surfactants—Fundamentals and Applications in the Petroleum Industry, L. Schramm editor, Cambridge Press (2000) p 209-214.
U.S. Pat. No. 4,733,728 to Morita, et al. Mar. 29, 1988 describes alkylether sulfonates prepared from alkoxylated alcohol or alkylphenol by reacting with sodium isethionate, propane sultone, or epichlorohydrin followed by reacting with sodium sulfite. Our invention differs from the prior art in several ways. The presence of a long hydrocarbon chain spacer between the last alkylene oxide and the terminal sulfonate group gives the products of our invention greater oil solubility and lower irritation properties. Stein, et al in U.S. Pat. Nos. 3,424,693 and 3,424,694 also uses a long chain hydrocarbon spacer that is also derived from an olefin sulfonic acid. Stein et al. however, does not use alkoxylates, as we do, and therefore these materials do not have the high electrolyte tolerance or hardness tolerance of our compositions. Also, our process of reacting an un-neutralized olefin sulfonic acid with the alkoxide of an alkoxylated alcohol, phenol or amine gives yields of >90% whereas Stein, et al. only get 10 to 50 mole percent. Finally, our invention and process does not require the use of toxic reactants such as epichlorohydrin, thionyl chloride, propane sultone or butane sultone that are used by the other reference cited from the prior art. These important differences will become apparent through the examples presented.